1. Field of the Invention
The invention relates to a magnetic resonance imaging apparatus including a main magnet having a frame with two magnetic elements having substantially parallel faces that face each other so as to define a gap between the magnetic elements, said magnetic elements comprising magnetic poles of opposite polarities for generating a static magnetic field in the gap, a supporting member for supporting said frame in a predetermined position relative to a substantially horizontal floor, and a patient support for supporting a patient so that a part of the patient that is to be examined is located in the gap.
2. Description of the Related Art
An example of an apparatus of this kind is disclosed in U.S. Pat. No. 5,008,624. In this known apparatus the faces that define the gap extend in the vertical direction. During an examination, the patient sits on a chair with a portion of his body located between the faces. A major advantage of this arrangement is that the magnet structure is open. This allows an easy access to the patient and causes less claustrophobia than conventionally designed magnets. In order to enable the examination of various parts of the patient's body, the magnet can be rotated about an axis that is parallel to the line connecting the faces and the chair can be lifted and tilted so as to support the patient at arbitrary angles with respect to the floor. It is a disadvantage of the known apparatus that the gap must be wide enough to accommodate the widest part of a patient. In other words, the gap must be at least as wide as the shoulder width of an adult person. However, it is very difficult and expensive to build a magnet having, in combination, a wide gap and a very homogeneous magnetic field with a high magnetic field strength in the gap.